Abstract
We have demonstrated that it is possible to reproducibly quantify hydrogen concentration in the SiN layer of a SiO2/SiN/SiO2 (ONO) stack structure using ultraviolet laser-assisted atom probe tomography (APT). The concentration of hydrogen atoms detected using APT increased gradually during the analysis, which could be explained by the effect of hydrogen adsorption from residual gas in the vacuum chamber onto the specimen surface. The amount of adsorbed hydrogen in the SiN layer was estimated by analyzing another SiN layer with an extremely low hydrogen concentration (<0.2 at. %). Thus, by subtracting the concentration of adsorbed hydrogen, the actual hydrogen concentration in the SiN layer was quantified as approximately 1.0 at. %. This result was consistent with that obtained by elastic recoil detection analysis (ERDA), which confirmed the accuracy of the APT quantification. The present results indicate that APT enables the imaging of the three-dimensional distribution of hydrogen atoms in actual devices at a sub-nanometer scale.
Highlights
Demands for the reliability of semiconductor devices, especially in the automotive industry, are continuously increasing.[1]
The accurate quantification of hydrogen has been very difficult because hydrogen atoms in the bulk or at the surface possibly diffuse during the analysis, or the amount of hydrogen atoms adsorbed from residual gas in the vacuum chamber onto the specimen surface is not always negligible.[10]
We have quantitatively estimated the concentration of hydrogen atoms in a SiN thin film with an ONO structure using atom probe tomography (APT)
Summary
Demands for the reliability of semiconductor devices, especially in the automotive industry, are continuously increasing.[1] Hydrogen atoms lead to severe degradation of reliability, such as negative bias temperature instability (NBTI)[2,3] and data retention properties in non-volatile memory.[4,5] a lack of methods for hydrogen concentration measurements using microscopy has veiled the degradation mechanism of device characteristics Conventional methods such as secondary ion mass spectrometry (SIMS),[6,7] nuclear reaction analysis (NRA)[8] and elastic recoil detection analysis (ERDA)[9] are successfully used to analyze hydrogen concentrations and distributions for blanket structures or structures larger than 100 μm. The accurate quantification of hydrogen has been very difficult because hydrogen atoms in the bulk or at the surface possibly diffuse during the analysis, or the amount of hydrogen atoms adsorbed from residual gas in the vacuum chamber onto the specimen surface is not always negligible.[10]
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